pwm: qpnp: Add support for configuring LPG to DTEST

LPG channel outputs can be configured to route them to DTEST
lines so that they can be made available externally on MPP or
GPIO pins. This will be helpful for testing the channel output.

CRs-Fixed: 705733
Change-Id: I8e04344fa1df677400bd4b2a50af5f0d04f1c346
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>